1. Field of the Invention
The present invention generally relates to liquid crystal display devices, and more particularly to a liquid crystal display device which has a matrix electrode structure to drive n.times.m pixels.
2. Description of Related Art
Japanese Laid-Open Patent Publication No. Hei-5-119746 describes a liquid crystal display with a matrix electrode structure. As the liquid crystal for the display, an anti-ferroelectric material is used. The anti-ferroelectric liquid crystal of this kind has at least one anti-ferroelectric state (the first stable state) and two ferroelectric states (the second and third stable states), and each of these states can be attained stably.
According to the disclosure of the above-mentioned publication, voltages applied to the liquid crystal panel are reversed periodically so that a direct current component is not applied to the panel. A transparent state of the panel is realized by using two ferroelectric states alternately, and a non-transparent state is realized by using the anti-ferroelectric state of the anti-ferroelectric liquid crystal.
The anti-ferroelectric liquid crystal panel shows different refractive anisotropies (.DELTA.n) between the two ferroelectric states when it is seen from slanting directions. Therefore, the display will flicker when the switching frequency between the two ferroelectric states becomes lower than, e.g., 30 Hz. The flicker of this kind is referred to as the slanting direction flicker. In order to eliminate the flicker, it is conceivable to choose a switching frequency which is higher than 30 Hz.
However, there is a certain limit in increasing the switching frequency in consideration of a response speed of the anti-ferroelectric liquid crystal, especially when a higher number of scanning electrodes is required to attain high definition of the display.
A proposal to prevent the slanting direction flicker has been made, for example, in Japanese Laid-Open Patent Publication No. Hei-4-311920. It proposes to switch the polarity of the applied voltage at a frequency which does not show the flicker during a holding period. However, since the holding voltage is switched or reversed at a same value, a brightness of the panel after the switching does not reach the brightness before the switching. This is because the anti-ferroelectric liquid crystal does not respond as quickly as the polarity changes. Therefore, the brightness of the panel changes every time the polarity is switched, and the flicker on the panel caused by the frequency rewriting pictures on the panel cannot be avoided.